How to get the most out of aerial imagery

Learning about a local farmer pioneering the use of satellite imagery for field management in 2004, Paul Overby soon began using the technology. Aerial imagery has been providing the North Dakota farmer with valuable insights on his fields since then, and Overby hasn’t looked back.

“Initially, I used satellite imagery to develop management zones on my fields. I have also used it for field scouting, especially in those early zone maps, to see if things matched up — ground truthing,” he says, adding that he continues to use imagery to monitor zones today.

Imagery has also been used for a retrospective look at yield maps when a section of a field didn’t look right. For example, he’s been able to go back and see the impact of a heavy rain on vegetation as a reason for losing yield in an area. Overby has also used it to identify an infestation of barley yellow dwarf for documentation for crop insurance loss on a wheat field.

Recently, he has been conducting more field trials and uses the imagery to monitor progress during the growing season.

“I am involved in the Data-Intensive Farm Management project with VRA N trials, so I used the images all season to see if there was an impact. I used imagery to monitor cover crop interseeding trials as well as seeding rate trials,” Overby says. “I also am looking at the impact of grazing on my pasture cells and trying to see the differences of cover crops based on seeding dates.”

Because it’s another source of data for decision making, Overby is willing to pay for the technology.

“Any management changes or adjustments should be monitored during the growing season, not just at the yield monitor. The information imagery provides is both informative and valuable,” he says. “It’s also fun to see the differences that show up, especially in field trials — or maybe I’m just a data nerd!”

Because the aerial imagery platform you choose depends on what you want to learn, it’s important that farmers understand the differences and applications among the three commonly used options, says Ryan Bergman, technical project specialist, Iowa State University. Pictured above are images from (left to right) an unmanned aerial vehicle, a manned aircraft, and a satellite.

Integrating Imagery

While Overby embraces the use of aerial imagery in his operation, growers who have not yet integrated it into their precision farming practices still consider it a novelty.

“Some farmers struggle with the return on investment,” says Ryan Bergman, technical project specialist, Iowa State University. “There can be instances where they invest in acquiring imagery, but they may not learn anything from it. Then the next time they use it, they may learn something important that justifies the expense.”

To get the most out of aerial imagery, Bergman says it is important farmers understand the differences and applications among the three commonly used options: satellite, manned aircraft, and unmanned aerial vehicle (UAV).

“The platform you choose really depends on what you want to learn,” he says.

Satellite Imagery

Available for decades, satellite imagery is a low cost source for crop health evaluation at the field level. Through the years, improvements to the timing and quality of imagery have been made, with many services offering image resolution as high as 1 meter.

“Satellite imagery is ideal for getting a high-level look at assessing things like field variability to understand what’s happening out there,” Bergman says. “With this type of imagery, you’ll be able to pick up differences from one planter pass to the next.”

The downside to imaging satellites is that many are still limited when it comes to revisit times; some provide revisit rates as much as five to 10 days apart. Depending on weather and cloud cover, that time can be even longer.

“Several overcast days could mean missing an image of your crop at an important growth stage,” he says.

Companies such as Planet are capturing multiple observations daily. In instances where cloud cover is an issue, this increases the likelihood you’ll get a cloud-free image each day.

“As resolution continues to increase and the ability to get images whenever we want improves, I think we’ll see satellite imagery grow in popularity,” Bergman says.

Cost is around 20¢ an acre.

“Many data management platforms offer free imagery as part of their programs,” he says. “However, the images tend to be a lower resolution — around the 3- to 10-meter range. But if you get them every week, they can still be valuable in helping you understand what’s happening across the field.”

The image (above) at 2-inch resolution, on the left, enables you to do stand counts earlier in the season and see individual plant leaves later in the season. At 20-inch resolution, on the right, row-to-row variations are visible.

Manned Flights

Bergman says manned aircraft, whose popularity seems to ebb and flow depending on whether there are good providers in an area, can show you row-to-row variability.

“This platform lets you pick out a single row within a planter and understand why a particular row is yellow compared with the row next to it that’s greener,” he says.

While the cost of hiring a manned aircraft is lower than owning a UAV, Bergman adds that targeting specific weather events or times of day is not easy because of the preparation required for each flight. He does point out, however, that many companies like Taranis offer packages that include multiple flights and field maps throughout the growing season for a fixed price. Costs can range from $1 to $5 per acre.

Unmanned Aerial Vehicle more recent entry to agriculture, UAV imagery gets you to the plant-to-plant variability level, which is where Bergman sees a lot of interest among farmers today.

“Typically, drones deliver the best image resolution, as they are equipped with high-quality cameras and can fly closer to the ground,” he says. “Imagery taken with a UAV can provide the ability to observe individual rows and plants. Drones also offer the best flexibility for timing.”

Bergman believes most drones are being used for crop scouting.

“If a grower wants to own a drone and use it for scouting, I think that’s a defined-use case that could justify the cost,” he says.

While Overby isn’t currently using a drone, he would like to eventually map out problem weeds, like Canada thistle or dandelion that need fall control, so he can spot spray affected areas.

“Prices are coming down, but the $2,000 to $3,000 cost for the drones I like are somehow not getting into my budget!” he says.

Whether drones are going to replace sprayers is a question Bergman fields a lot.

“A drone’s ability to cover acres quickly like a self-propelled sprayer can just isn’t there, even when you start swarming them,” he says. “A co-op with a well set up tending system can cover 800 acres in a day if it needs to. It’s going to be hard to do that with a drone. However, spot spraying and hard-to-get-to areas will continue to grow for drone use.”

Bergman also cautions users to be aware of the legal requirements for owning and operating a UAV. 

“For example, airports have flight restrictions around them. Where we’re located in Ames, Iowa, a lot of our fields have requirements we have to follow because we’re within a couple miles of an airport,” he says.

Picking a Platform

Before deciding on an aerial imagery source, the following four questions should be asked.

1. What resolution will clearly show an issue in a field? “Because the platform you choose is guided by what you want to learn, resolution is the No. 1 driver for which source you go with,” says Ryan Bergman, technical project specialist, Iowa State University.
2. What will the image be used for?
3. Is timing critical?
4. What is the cost? The cost difference between each platform can be significant, especially if a company is packaging imagery with other products associated with the data.